1. Field of the Invention
This invention relates to a method for applying a coating to a surface of a workpiece, using electro-photography, wherein a support with a photoconductive layer is provided with an electrostatic charge image, wherein a coating material is applied to the carrier by using electrostatic force, and wherein the coating material is applied to the workpiece to be coated.
2. Description of Related Art
A method known from European Patent Reference EP 0 647 885 A1 is used for imprinting ceramic and glass products. A toner is used as the coating material, and the toner particles have a pigment core. The pigment core is made of ceramic pigments and is surrounded by a binder resin shell. Charge control agents are connected to the binder resin shell. With an electrostatic copying process the toner is applied on a paper coated with gum arabic. A clear lacquer is applied to the coated paper for fixing. Thereafter, the paper can be placed on the ceramic or glass product to be coated and can be wetted. The paper can then be pulled off, while the gum arabic layer and the colored coating applied to the gum arabic layer adhere to the ceramic or glass product. This is finally followed by a firing process, wherein the color pigments melt together with the surface of the ceramic or glass product. With this process it is possible to apply high-quality, particularly scratch-resistant coatings to a workpiece. However, only such workpieces can be coated which can withstand the firing process without damage.
Coating materials are also known, which have a thermoplastic material as the basic material, which melts at low temperatures. The thermoplastic material is mixed with color pigment and charge control agents. This coating material is applied by an electrostatic printing process to a paper to be coated. The coated paper is finally fixed at a temperature approximately between 90xc2x0 C. and 170xc2x0 C. A coating thus produced is sensitive to mechanical effects.
It is one object of this invention to provide a method of the type mentioned above but wherein qualitatively high-grade surfaces can be produced.
This object is achieved with at least the duromer components resin and hardener applied as the coating material to the carrier together or one after the other. With this process, duromer coatings can be applied to workpieces in a simple manner. These coatings have a high surface quality and in particular are scratch-resistant and temperature-proof.
In accordance with one embodiment of this invention, the hardener is stored together with the resin in a storage container in the form of material particles, the material particles are doped with charge carriers, and the material particles, together with the charge carriers, are electrostatically applied to the carrier.
Alternatively, the hardener and the resin are stored separately from each other in the form of hardener or resin particles in storage containers, the resin and the hardener particles are doped with charge carriers, and the material particles are electrostatically applied to the carrier by the charge carriers.
With the method of this invention, it is possible to attribute defined properties to the coating. This is possible if fillers and/or coloring agents and/or additives are mixed with the coating material. The fact that the coating material can be used as a xe2x80x9cvehiclexe2x80x9d for defined materials is useful. Accordingly, the vehicles convey the materials to the workpiece and fix them on the surface of the workpiece.
To fix the applied coating material, it can polymerize under the reaction of temperature and/or pressure.
In one embodiment of this invention, the coating material is applied to a planar intermediate carrier having an adhesive layer, the intermediate carrier is placed with its coated side on the workpiece and following the placement of the intermediate carrier on the workpiece, the adhesiveness of the coating material is cancelled and then the intermediate carrier is lifted off the workpiece.
Thus it is initially possible to produce patterns, similar to decals, which can be applied at a later time to the workpiece to be coated. For example, this has advantages if there is a difference in the locality of the actual workpiece production and the electro-photographic coating generation.
Gum arabic, wax or silicon can for example be applied to the intermediate carrier as the adhesive layer. Thus it is possible to cancel the adhesion between the intermediate carrier and the coating material using water with the gum arabic, and by the application of heat with wax. Different materials can be employed as intermediate carriers. For example, an intermediate carrier made of paper or cardboard can be used.
To prevent the possibility of damage to the coating material by mechanical effects when an intermediate carrier is transported, a protective layer, for example a lacquer layer, can be applied over the coating material.